The present invention relates to fluid control valves.
More particularly, the invention provides an improved diaphragm useful for a large hydraulically-operated valve or pressure regulating valve of the type used in pipelines to transport water, oil, gas, acids, alkalis and other fluids.
Although valves can be installed and operated in any position, in the present specification the term lower refers to the side of the diaphragm always in contact with the fluid being transported. Upper refers to the opposite side of the diaphragm which may be in contact with a fluid to control opening/closing of the valve.
Small fluid control valves are easily actuated by hand, foot, machine, solenoid or pilot air. Large valves, about 8″ or more, are more difficult to operate, particularly when the fluid being transported is at high pressure, because the forces needed to prevent flow increase as the square of the pipeline diameter. A well known solution to the problem is to use the fluid being transported as an actuator, to form a hydraulically-operated diaphragm valve. A diaphragm valve has the advantage of not requiring a stuffing box, and operating leak-free for the life of the diaphragm.
Typically the diaphragm valve is operated by directing hydraulic pressure into/out of a chamber on the upper side of the diaphragm. In some designs a steel compression spring is used in the upper chamber to ensure closure of the valve when needed. When the valve is to be opened, pressure in the upper chamber is reduced and the fluid being handled pushes open the diaphragm for the resumption of flow.
Clearly it is highly desirable that the valve diaphragm operates for the largest possible number of cycles and the longest possible time period. The cost of a failed diaphragm goes far beyond the cost of a replacement, as leakage needs to be controlled, a technician needs to be sent to the site and the pipeline may need to be shut down during replacement of the failed component.
Hydraulically-operated diaphragm valves are known and in use.
Newberg discloses a diaphragm valve in International Publication WO 02/066876 A1. The valve is operated by manually turning a control cylinder which operates a screw mechanism to raise or lower a sealing element extending from a diaphragm. Valves of this type are appropriate only for small diameter conduits, as the valve is hand, not hydraulically operated.
Some designs, for example the Elastomeric Element Valve disclosed by Walton et al. in U.S. Pat. No. 6,102,071, employ a metal coil compression spring to assist in valve closure. Such spring was considered necessary in a hydraulically-operated valve because when both the upper chamber and the passages leading to/from the pipeline are at the same pressure, there is no substantial force available to close (lower) the diaphragm. The problem with this design is that at small pressure differences and low flow rates the metallic spring causes vibrations which quickly damage the diaphragm, thus making the valve inoperable. A further drawback of the design is the pressure drop caused by the spring in the pipeline during normal open-valve operation. Yet a further problem is that after such valve has been left open for an extended period, the valve is very difficult to close, due to loss of elasticity in the elastomer at the sharp bend proximate to the maximum operating diameter of the diaphragm.
In response to these difficulties the present inventor developed a new design first disclosed 30 Apr. 1993 in Israel Patent No. 119,963. The distinctive feature of this design is the presence above its concave surface of radial and circular ribs urging the diaphragm into its closed (lower) position without requiring a steel coil compression spring for this purpose. This design proved to be effective for smaller valves, in the range ½″ to 8″ (13–203 mm). However valves larger than 8″ required ribs on the concave surface which were wide and high. Furthermore the strong closing force generated by these ribs produced an unacceptable pressure loss in the pipeline wherein the valve was installed.
The difficulties experienced with the diaphragm described in Israel Patent No. 119,963 were overcome by the Spring Diaphragm for Shut-Off Valves and Regulators disclosed by the present inventor in U.S. Pat. No. 6,095,484. A two-part diaphragm has an upper and a spaced-apart lower tier. The lower tier functions as a conventional diaphragm. The upper tier forms a resilient disk urging the lower part towards its closed (lower) position. Both parts are provided with ribs. This design was tested and found to meet all operational and reliability requirements. However, manufacturing cost was too high in view of the sharp competition existing in the field of hydraulic valves.